Atmospheric processes

Abstract:

Abstract:

Abstract. The Atlantic Multidecadal Variability (AMV) and the North Atlantic Oscillation (NAO) are the dominant modes of oceanic and atmospheric variability in the North Atlantic, respectively, and are key sources of predictability from seasonal to decadal timescales. However, the physical processes and feedback mechanisms linking the AMV and NAO, and the role of diabatic processes in these feedbacks, remain debated. We present a data-driven dynamical modelling framework which captures coupled decadal variability in AMV, NAO, and North Atlantic precipitation. Applying equation discovery methods to observational data, we identify low-order models consisting of three coupled ordinary differential equations. These models reproduce observed decadal variability and show robust out-of-sample predictive skill on multi-annual to decadal lead times. The resulting model dynamics include a distinct quasi-periodic 20-year oscillation consistent with a damped oceanic mode of variability. Notably, precipitation-related terms feature prominently in the low-order models, suggesting an important role for latent heat release and freshwater fluxes in mediating ocean–atmosphere interactions. We propose new feedback mechanisms between North Atlantic sea surface temperature and the NAO, with precipitation acting as a dynamical bridge. Overall, these results illustrate how equation discovery can provide mechanistic hypotheses and new insight beyond conventional analyses of observations and climate model simulations.

Abstract:

Large quantities of plastic pollution are accumulating at small island nations across the western Indian Ocean. Despite a historical focus on terrestrial inputs, recent research suggests that most pollution arriving at some islands may come from fishing and shipping activity. We use a 2D Lagrangian particle-tracking model, combined with satellite-tracked shipping and fishing data, to identify major fisheries and shipping lanes which are responsible for plastic debris beaching at the Seychelles. Virtual particles, representing plastic debris, are released monthly over multiple decades and are advected by currents from a 1/50°(∼2 km) regional ocean model. We find most fishing debris originates from within the Seychelles' own exclusive economic zone, and sources of shipping debris are concentrated along major shipping routes. Sources vary seasonally, due to wind-induced reversals of surface currents between monsoons. Finally, we find variation in the quantity and seasonality of debris accumulation on a sub-island scale. Therefore, higher-resolution models that resolve local currents and kilometre scale islands may play a vital role in clean-up and management efforts.